Field of the Invention
The invention relates to particle-optical systems using multiple beamlets of charged particles, such as an electron microscopy apparatus and electron lithography apparatus.
Further the invention relates to particle-optical components and arrangements which may be used in particle-optical systems using multiple beamlets of charged particles; the particle-optical components are, however, not limited in the application to systems using multiple beamlets. Such particle-optical components may be used in particle-optical systems using only one single beam of charged particles or plural beams or beamlets of charged particles.
The invention may be applied to charged particles of any type, such as electrons, positrons, myons, ions and others.
Brief Description of Related Art
A conventional particle-optical system is known from U.S. Pat. No. 6,252,412 B1. The electron microscopy apparatus disclosed therein is used for inspecting an object, such as a semiconductor wafer. A plurality of primary electron beams is focused in parallel to each other on the object to form a plurality of primary electron spots thereon. Secondary electrons generated by the primary electrons and emanating from respective primary electron spots are detected. For each primary electron beam a separate electron beam column is provided. The plurality of separate electron beam columns is closely packed to each other. A density of the primary electron beam spots formed on the object is limited by a remaining foot step size of the electron beam columns forming the electron microscopy apparatus. Thus, also the number of primary electron beam spots which may be found at the same time on the object is limited in practice resulting in a limited throughput of the apparatus when inspecting semiconductor wafers of a high surface area at a high resolution.
From U.S. Pat. No. 5,892,224, US 2002/0148961 A1, US 2002/0142496 A1, US 2002/0130262 A1, US 2002/0109090 A1, US 2002/0033449 A1, US 2002/0028399 A1, there are known electron microscopy apparatuses using a plurality of primary electron beamlets focused on the surface of the object to be inspected. The beamlets are generated by a multi-aperture plate having a plurality of apertures formed therein, wherein an electron source generating a single electron beam is provided upstream of the multi-aperture plate for illuminating the apertures formed therein. Downstream of the multiple-aperture plate a plurality of electron beamlets is formed by those electrons of the electron beam passing the apertures. The plurality of primary electron beamlets is focused on the object by an objective lens having an aperture which is passed by all primary electron beamlets. An array of primary electron spots is thus formed on the object. Secondary electrons emanating from each primary electron spot form a respective secondary electron beamlet, such that also a plurality of secondary electron beamlets corresponding to the plurality of primary electron beam spots is generated. The plurality of secondary electron beamlets pass the objective lens, and the apparatus provides a secondary electron beam path such that each of the secondary electron beamlets is supplied to a respective one of a plurality of detector pixels of a CCD electron detector. A Wien-filter is used for separating the secondary electron beam path from a beam path of the primary electron beamlets.
Since one common primary electron beam path comprising the plurality of primary electron beamlets and one common secondary electron beam path comprising the plurality of secondary electron beamlets is used, one single electron-optical column may be employed, and the density of primary electron beam spots formed on the object is not limited by a foot step size of the single electron-optical column.
The number of primary electron beam spots disclosed in the embodiments of the above mentioned documents is in the order of some ten spots. Since the number of primary electron beam spots formed at a same time on the object limits the throughput, it would be advantageous to increase the number of primary electron beam spots for achieving a higher throughput. It has been found, however, that it is difficult to increase the number of primary electron beam spots formed at a same time, or to increase a primary electron beam spot density, employing the technology disclosed in those documents while maintaining a desired imaging resolution of the electron microscopy apparatus.
It is therefore an object of the present invention to provide particle-optical systems using charged-particle beamlets of an increased density and allowing to manipulate the charged-particle beamlets with an increased accuracy.
It is a further object of the present invention to provide particle-optical components for manipulating beams and beamlets of charged particles with an increased accuracy.